So me and my family have this theory
Me, my brother, and my dad have this theory that since, across multiple sci-fi fandoms, everyone (even the aliens) speak English, that therefore means that something must have caused them to do that, right? We figured it couldn't have been chance, or a trading language, since they hate each others' guts.
So therefore we theorised that there must have been some sort of Empire, right?
So that means we figured that there was once a mighty 2nd British Empire that ruled many multiverses, that eventually fell and gave way to all these different empires that, despite being bitter enemies, still speak British English simply because it is the common language and had been the common language since time immemorial, all due to a certain 2nd British Empire.
But before you go arguing, just as an FYI, this is all a silly little joke that got out of hand.